Engineering iron single atomic sites with adjacent ZrO2 nanoclusters via ligand–assisted strategy for effective oxygen reduction reaction and high–performance Zn–air batteries

Atomically dispersed iron–nitrogen–carbon (Fe–N–C) catalyst is a promising candidate to replace Pt for oxygen reduction reaction (ORR). To enhance ORR activity of Fe–N–C catalysts, the density and distribution of isolated Fe–N4 sites should be further optimized. Herein, a ligand–assisted strategy to synthesis of single atomic Fe–N–C derived from Zr–metal–organic frameworks (Zr–MOFs) is proposed. During preparation, –NO2 (from 2–nitroterephthalic acid ligands) in Zr–MOFs not only acts as the anchoring sites to capture Fe–polydopamine (FePDA) source but also plays a crucial role in modulating the Fe − N4 configuration. The resulting SA Fe@ZrO2/NC catalyst consists of FeN4 sites with adjacent ZrO2 in N–doped carbon, in which in–situ introduction of ZrO2 positively enhance O2 adsorption ability. Due to the moderate pore structure, atomically dispersed Fe–N4 active sites, and the strong interface interaction between isolated Fe atoms and ZrO2 nanocluster, the as–prepared catalyst exhibits comparable ORR activity and outstanding stability in alkaline solution. When assembled in a rechargeable Zn–air battery, the battery with SA Fe@ZrO2/NC air electrode delivers a stable open circuit voltage, high–power density (250 mW cm−2) and discharge specific capacity (730 mA h gZn−1). It also demonstrates a long cycle life and good rate performance. Density functional theory calculation results reveals that the adjacent ZrO2 nanocluster modulates the electron structure of Fe atoms in FeN4 sites with an improved ORR process and activity. This work provides a facile strategy for preparing efficient single atomic Fe–N–C catalyst to drive the oxygen reduction reaction in Zn–air batteries.